Effort Comparison - Plot momentary speed instead of time lag
Instead of presenting the accumulated time lag, calculate the average speed of each sub-segment (total length divided by 20, for example, or a minimal track length to produce meaningful results).
The problem with the current time lag is that the segment is not uniform, one section can have a certain grade, followed by a steeper grade. Trying to compare 2 riders, it would appear that the slower rider is gaining on the faster rider when the slow rider is still on the less steep section, while the faster is slowing. It would be more valuable to see the difference in the fast section and slow sections.
The X axis would remain the distance on the segment, but there will be a plot for each rider, representing the localized sub-segment speed. Maybe the user could choose the sub segment size, based on the quality of the plot (small segments are ideal, but depends on the GPS update rate and accuracy, the outcome might be very jittery).